Process for the preparation of borosilicate zeolites

ABSTRACT

Novel crystalline ZBH borosilicate zeolites of the pentasil type are prepared by hydrothermal crystallization of silicon dioxide and boric acid in the presence of alkali metal salts, at from 80° to 140° C. in an ethereal or aqueous-ethereal mixture.

The present invention relates to novel ZBH borosilicate zeolites and to a process for the preparation of crystalline ZBH borosilicate zeolites of the pentasil type in a pure or aqueous etherel medium, without the use of amines, and to the use of the products as catalysts for converting methanol or dimethyl ether to lower olefins.

Boron zeolites have hitherto not been found in nature. They can only be obtained synthetically (German Laid-Open Application DOS No. 2,746,790). Aluminum-containing zeolite materials, both of natural and of synthetic origin, have proved catalytically active in various types of hydrocarbon conversions, for example in hydrocarbon cracking technology, and are also used industrially as ion exchangers and molecular sieves.

In general, zeolites have a highly ordered structure with a rigid three-dimensional lattice of SiO₄ and MeO₄ tetrahedra, Me being, for example, Al, Fe, Ga and B. These tetrahedra are linked by shared oxygen atoms and the ratio of Si and Me atoms to oxygen is 1:2.

The electrovalency of the tetrahedra containing the trivalent element Me is balanced by inclusion of cations, for example alkali metal cations or hydrogen ions, in the crystal. Cation exchange is feasible. Before drying or calcining, the voids between the tetrahedra are occupied by water molecules.

In recent years, crystalline aluminosilicates having a high SiO2/Al203 ratio, namely ≧11, have aroused increasing interest. Such zeolites have a pentasil structure and are distinguished by great heat stability and extremely high acidity. They are synthesized in a conventional manner from a silicon component and an aluminum component in the presence of bulky quaternary organic ammonium or phosphonium compounds and alkali metal compounds as mineralizing agents. Such a process is described in U.S. Pat. No. 3,702,886. The large ammonium or phosphonium ions are intended to serve as a template for the desired zeolite structure and permit the synthesis of aluminum zeolites having SiO₂ /Al₂ O₃ ratios of, for example, from 100 to 3000.

Boron zeolites having a pentasil structure have hitherto only been prepared in the presence of amines (German Laid-Open Application DOS No. 2,746,790). The use of the quaternary amines presents technical problems.

We have found that novel ZBH borosilicate zeolites of the pentasil type are obtained by hydrothermal crystallization of silicon dioxide and boric acid in the presence of alkali metal salts if the crystallization is carried out at from 80° to 140° C. in an ethereal or aqueous-ethereal mixture.

In a preferred embodiment of the preparation of these amine-free ZBH borosilicate zeolites a reaction mixture of SiO₂, for example a commercial pyrogenic silica, H₃ BO₃ and NaOh is reacted in a 50:50 (by weight) ether/water mixture for from 5 to 7 days at 110°-130° C. in a stirred autoclave under autogenous pressure. The reaction product first obtained may, before calcining, contain ether in place of the H₂ O molecules in the intracrystalline pores. All residues of organic compounds are removed by drying and calcining, so that only the free alkali metal ions remain in the zeolite.

The molar ratio of SiO₂ to B₂ O₃ in the reaction mixture is from 3 to 300, preferably from 10 to 50.

The proportion of alkali metal hyroxide is from 1 to 3 moles, preferably about 1.7 moles, per molar equivalent of B₂ O₃.

Advantageously, nucleating crystals are added to control and accelerate the reaction.

The solvents used are the general category of ethers, including linear and cyclic esters containing a (--CH₂ --CH₂ --O--) group, e.g. monoethylene, diethylene, triethylene and tetraethylene glycol dimethyl ether, diethyl ether, tetrahydrofuran, dioxane or a mixture of triethylene to decaethylene glycol methyl isopropyl ether having a mean degree of oxyethylation of 5.5 and hence an average formula of CH₃ O--(CH₂ --CH₂ --O)₅.5 --C₃ H₇, diethylene glycol methyl isopropyl ether or a mixture of polyethylene glycol methyl isopropyl ethers having a mean degree of oxyethylation of 5.5 and hence the average formula CH₃ O(--CH₂ --CH₂ --O)₅.5, or a mixture of oxyethylated oxo-alcohols having a mean molecular weight of 200, 600 or 6,000, as well as linear ethers containing a (CH₃ --CH--CH₂ --O) group, and linear ethers containing a (--CH₂ --O) group, e.g. dimethoxymethane. The glymes give particularly well-formed crystals of the ZBH-boron zeolites, of size 1-5 μm. This is a further advantage of the novel method of preparation in ethers.

The molar composition of the reaction mixture is set to conform to the following values:

SiO₂ /B₂ O₃ =3-300, preferably 10-50

M₂ O/B₂ O₃ =>1, preferably 1.3-2

ROR/B₂ O₃ =18-390

wherein M is an alkali metal, especially Na, and ROR is an ether. The concentration of the ether in H₂ O may be from 10 to 100% by weight, preferably 50% by weight.

The process according to the invention is carried out at reaction temperatures of from 80° to 140° C., preferably from 110° to 130° C., advantageously under autogenous pressure in a stainless steel stirred autoclave for from 3 to 7 days.

After the reaction, the product is advantageously filtered off, washed thoroughly with water and dried at 110° C. for 16 hours. It is then calcined at 550° C. for 20 hour in order to burn off the ether still occluded, and dehydrate the zeolite. The alkali metal form of the zeolite can be converted to the catalytically active H form by conventional exchange methods, for example using ammonium salts. The mother liquor separated off can be re-used in subsequent syntheses.

The general formula of the ZBH borosilicate zeolites prepared by the method of the invention is:

    M.sub.2/n O:B.sub.2 O.sub.3 : x SiO.sub.2 :y H.sub.2 O

where M is one or more cations of valency n, x is ≧10 and y is from 0 to 80.

The ZBH borosilicate zeolites prepared in ether, in accordance with the invention, exhibit the following important X-ray diffraction lines:

                  TABLE 1                                                          ______________________________________                                         Interplanar Relative   Interplanar                                                                              Relative                                      spacing     intensity  spacing   intensity                                     d (Å)   I/I°                                                                               d (Å) I/I°                                   ______________________________________                                         11.0746 ± 0.15                                                                          100        2.9259    7                                             9.9725      68         2.8543    4                                             9.7271      19         2.7151    5                                             6.6567      10         2.5928    5                                             6.3220      17         2.4984    3                                             5.9489 ± 0.1                                                                            22         2.4746    5                                             5.6740      11         2.4013    4                                             5.0022      10         2.3106    3                                             4.9479      10         1.9999    10                                            4.5883       8         1.9825    9                                             4.3352      10         1.9418    3                                             4.2392      11         1.9062    3                                             3.9747 ± 0.07                                                                            5         1.8621    5                                             3.8322      96         1.8289    3                                             3.7980      70         1.7576    3                                             3.7282      30         1.6615    3                                             3.6940      46         1.6544    3                                             3.6254      25         1.6501    3                                             3.4652       5         1.4807    3                                             3.4174       9         1.4539    4                                             3.3654       6         1.4377    4                                             3.3371      10         1.4149    4                                             3.2907      10         1.4046    3                                             3.2429       3         1.3864    4                                             3.1188       4         1.3738    4                                             3.0303      12         1.3556    3                                             2.9691      13                                                                 ______________________________________                                    

The X-ray diffraction diagram is recorded using an automatic APO-10 powder diffractometer. Copper radiation, and a graphite monochromator, are used.

The X-ray diffraction pattern typical for the ZBH borosilicate zeolites prepared in ether proves these products to be members of the pentasil family.

In the novel ZBH borosilicate zeolites the boron is built into the tetrahedral lattice positions of the crystal. The incorporation of boron into the crystal lattice manifests itself in a shift in the X-ray diffraction lines towards smaller d-values compared to corresponding aluminosilicate zeolites (Table 2); the length of a B--0 bond is substantially shorter than the Al--O spacing. Hence, incorporating boron into the crystal lattice results in a contraction of the unit cell, i.e. a shift in the d spacings to smaller values compared to the corresponding aluminosilicate zeolites or compared to the silicalite.

A comparison of the lattice plane spacings of the novel boron zeolites with those of ZSM-5 shows that the d values (Å) in the former are smaller than in the latter (cf. Table 2).

                  TABLE 2                                                          ______________________________________                                         ZBH               ZBH                                                          d         I/I         d         I/I                                            ______________________________________                                         11.0746   100         2.9259    7                                              9.9725    69          2.8543    4                                              9.7271    19          2.7151    5                                              6.6567    10          2.5928    5                                              6.3220    17          2.4984    3                                              5.9489    22          2.4746    5                                              5.6740    11          2.4013    4                                              5.5405    18          2.3831    5                                              5.0022    10          2.3106    3                                              4.9479    10          1.9999    10                                             4.5883     8          1.9825    9                                              4.3352    10          1.9418    3                                              4.2392    11          1.9062    3                                              3.9747     5          1.8621    5                                              3.8322    96          1.8289    3                                              3.7980    70          1.7567    3                                              3.7282    30          1.6615    3                                              3.6940    46          1.6544    3                                              3.6254    25          1.6501    3                                              3.4652     5          1.4807    3                                              3.4174     9          1.4539    4                                              3.3654     6          1.4377    4                                              3.3371    10          1.4149    4                                              3.2907    10          1.4046    3                                              3.2429     3          1.3864    4                                              3.1188     4          1.3738    4                                              3.0303    12          1.3556    3                                              2.9691    13                                                                   ______________________________________                                                           AMS-1 B.sup.(2)                                              ZSM-5.sup.(1)               Relative                                           d(A)      I           d (Å) Intensity                                      ______________________________________                                         11.36     s           11.3 ± 38.2                                           10.20     ms          10.1 ± 0.2                                                                            30                                             9.90      --          6.01 ± 0.07                                                                           14                                             9.14      vw          4.35 ± 0.05                                                                           11                                             7.54      w           4.26 ± 0.05                                                                           14                                             7.17      w           3.84 ± 0.05                                                                           100                                            6.79      vw          3.72 ± 0.05                                                                           52                                             6.06      w           3.65 ± 0.05                                                                           31                                             5.77      w           3.44 ± 0.05                                                                           14                                             5.63      w           3.33 ± 0.05                                                                           16                                             5.42      vw          3.04 ± 0.05                                                                           16                                             5.19      vw          2.97 ± 0.02                                                                           22                                             5.05      w           2.48 ± 0.02                                                                           11                                             4.65      w           1.99 ± 0.02                                                                           20                                             4.40      w           1.66 ± 0.02                                                                           12                                             4.30      w                                                                    4.12      vw                                                                   4.04      vw                                                                   3.84      vs                                                                   3.74      vs                                                                   3.62      s                                                                    3.50      w                                                                    3.46      w                                                                    3.33      w                                                                    3.27      vw                                                                   3.07      w                                                                    3.00      m                                                                    ______________________________________                                          .sup.(1) Zeolites and molecular sieves, Donald W. Breck, WileyInterscienc      Publishers, page 373 (1974)                                                    .sup.(2) German LaidOpen Application DOS 2,746,790, Standard Oil Co.     

The crystalline ZBH borosilicate zeolites described here differ clearly in respect of their interplanar spacings (d values in Å) from those of boron zeolite AMS - 1 B of Standard Oil Co. (Table 2).

A comparison of the intensities of the X-ray diffraction lines also reveals substantial differences. The differences in both d values and intensities prove that the ZBH borosilicates are novel zeolites.

It is true that the ZBH borosilicate zeolites prepared in ethers belong, in respect of structural type, to the pentasil family, but compared to the other members of this structural type they exhibit markedly different X-ray diffraction lines and hence different lattice spacings.

The zeolites, obtained in H form after exchange, can be extruded together with a matrix material and be employed as catalysts for hydrocarbon conversions such as isomerizations, cracking and conversion of alcohols and ethers.

The analytical data in the Examples relate to dry material. The substances are calcined for 20 h at 550° C. before chemical analysis. The difference from 100% is accounted for by adsorbed water.

EXAMPLES 1-6

80 g of aerosil are stirred into 1,000 g of a 50:50 ether/H₂ O mixture at about 40° C. 15.2 g of H₃ BO₃ are dissolved in 200 g of the ether/H₂ O mixture and the two solutions are then combined. 14.7 g of NaOH are then added, followed, if desired, by nucleating crystals. The mixture, stirred to homogenize it, is reacted for 5 days at from 80° 140° C. in a stirred autoclave under autogenous pressure. It is then cooled and the crystalline product is filtered off, washed with 10 liters of water, dried for 16 hours at 110° C. and calcined for 20 hours at 500° C.

The results of Examples 1 to 6, employing different solvents, are summarized in Table 3. The synthetic boron zeolites were obtained free from impurities.

Table 4 shows the series of Examples and the X-ray diffraction diagrams of the zeolites, as obtained using various solvents.

EXAMPLE 7-8

Examples 7 and 8 (Table 5) show the results of preparing crystalline boron-aluminosilicates in diethylene glycol dimethyl ether, using various SiO₂ /B₂ O₃ ratios.

                                      TABLE 3                                      __________________________________________________________________________                            SiO.sub.2 /B.sub.2 O.sub.3                                                     ratio % SiO.sub.2                                                                         % B.sub.2 O.sub.3                                                                   SiO.sub.2 /B.sub.2 O.sub.3                                                           % Na                              Example                                                                             Ether             employed                                                                             found                                                                               found                                                                               found found                             __________________________________________________________________________     1    Ethylene glycol dimethyl ether                                                                   11    86.6 4.58 22.1  4.3                               2    Diethylene glycol dimethyl ether                                                                 11    87.6 3.5  29.2  3.1                               3    Triethylene glycol dimethyl ether                                                                11    79.7 8.28 11.3  7.2                               4    Tetraethylene glycol dimethyl ether                                                              11    89.3 3.6  29.0  4.0                               5    CH.sub.3 O--(CH.sub.2 --CH.sub.2 --O).sub.5.5 --C.sub.3 H.sub.7                                  11    92.8 1.17 92.6  3.05                              6    CH.sub.3 O--(CH.sub.2 --CH.sub.2 --O).sub.2 --C.sub.3 H.sub.7                                    11    85.0 6.18 16.0  3.86                              __________________________________________________________________________

                                      TABLE 4                                      __________________________________________________________________________     Example 1                                                                               Example 2                                                                               Example 3                                                                               Example 4                                                                               Example 5                                                                               Example 6                         d(Å)                                                                            4.2354                                                                             d(Å)                                                                            I/I°                                                                        d(Å)                                                                            I/I°                                                                        d(Å)                                                                            I/I°                                                                        d(Å)                                                                            I/I°                                                                        d(Å)                                                                            I/I°                  __________________________________________________________________________     11.0239                                                                             92  11.0746                                                                             100 10.9615                                                                             65  10.8451                                                                             11  11.0877                                                                             82  10.9802                                                                             88                           9.9244                                                                              65  9.9725                                                                              68  9.8165                                                                              52  9.9248                                                                              63  9.9659                                                                              66  9.8640                                                                              63                           9.6520                                                                              22  9.7271                                                                              19  6.2778                                                                              17  9.6640                                                                              20  9.7499                                                                              20  6.6145                                                                              8                            6.2968                                                                              15  6.6567                                                                              10  5.9070                                                                              18  6.6645                                                                              8   6.3307                                                                              15  6.2757                                                                              15                           5.9453                                                                              17  6.3220                                                                              17  4.9255                                                                              14  6.3294                                                                              13  5.9459                                                                              19  5.9344                                                                              21                           5.6705                                                                              12  5.9489                                                                              22  4.5591                                                                              15  5.9518                                                                              19  5.6699                                                                              10  5.6334                                                                              11                           5.5216                                                                              15  5.6740                                                                              11  3.8114                                                                              100 5.6628                                                                              10  5.5449                                                                              14  5.5386                                                                              14                           4.9889                                                                              9   5.5405                                                                              18  3.7773                                                                              74  5.5281                                                                              17  4.9861                                                                              10  5.0769                                                                              4                            4.9403                                                                              8   5.0022                                                                              10  3.6831                                                                              54  4.9904                                                                              11  4.6151                                                                              9   4.9609                                                                              10                           4.5789                                                                              10  4.9479                                                                              10  3.6514                                                                              22  4.9372                                                                              8   4.5917                                                                              11  4.9298                                                                              9                            4.4317                                                                              6   4.5883                                                                              8   3.4392                                                                              34  4.5813                                                                              8   4.3479                                                                              17  4.5711                                                                              7                            4.3356                                                                              12  4.3352                                                                              10  3.4083                                                                              38  4.5354                                                                              12  3.8365                                                                              100 4.3218                                                                              10                           4.2248                                                                              13  4.2392                                                                              11  3.3848                                                                              32  3.9794                                                                              6   3.8026                                                                              63  4.2193                                                                              13                           3.9758                                                                              6   3.9747                                                                              5   3.3482                                                                              37  3.8282                                                                              100 3.7027                                                                              46  3.9654                                                                              6                            3.8218                                                                              100 3.8322                                                                              96  3.3178                                                                              34  3.7949                                                                              73  3.6328                                                                              25  3.8215                                                                              100                          3.7928                                                                              71  3.7980                                                                              70  3.2976                                                                              27  3.6941                                                                              51  3.4261                                                                              20  3.7915                                                                              70                           3.6911                                                                              50  3.7282                                                                              30  3.2803                                                                              24  3.6275                                                                              27  3.4055                                                                              20  3.6864                                                                              47                           3.6255                                                                              29  3.6940                                                                              46  3.2514                                                                              20  3.4508                                                                              7   3.3895                                                                              19  3.6154                                                                              29                           3.4524                                                                              9   3.6254                                                                              25  3.0179                                                                              18  3.4165                                                                              9   3.3754                                                                              19  3.4486                                                                              7                            3.4173                                                                              12  3.4652                                                                              5   2.9612                                                                              18  3.3287                                                                              10  3.3538                                                                              30  .4141                                                                               8                            3.3517                                                                              12  3.4174                                                                              9   2.9443                                                                              16  3.2877                                                                              10  3.3330                                                                              25  3.3737                                                                              6                            3.3237                                                                              14  3.3654                                                                              6   2.0532                                                                              8   3.0288                                                                              11  3.3207                                                                              21  3.3563                                                                              6                            3.2935                                                                              13  3.3371                                                                              10  1.9936                                                                              12  2.9706                                                                              12  3.2989                                                                              20  3.3223                                                                              10                           3.0295                                                                              12  3.2907                                                                              10  1.9718                                                                              10  2.9519                                                                              11  3.2763                                                                              14  3.2823                                                                              11                           2.9667                                                                              14  3.2429                                                                              3   1.8542                                                                              8   2.9199                                                                              10  3.2483                                                                              11  3.0269                                                                              12                           2.9206                                                                              11  3.1188                                                                              4   1.8369                                                                              9   2.8500                                                                              4   3.0278                                                                              9   2.9642                                                                              14                           2.7145                                                                              6   3.0303                                                                              12  1.4508                                                                              5   2.5901                                                                              5   2.9764                                                                              14  2.9233                                                                              8                            2.5969                                                                              5   2.9691                                                                              13           2.5490                                                                              3   2.9662                                                                              11  2.8453                                                                              3                            2.4732                                                                              6   2.9259                                                                              7            2.4718                                                                              5   2.9224                                                                              9   2.7149                                                                              5                            2.4015                                                                              5   2.8543                                                                              4            2.4023                                                                              4   2.7229                                                                              6   2.5863                                                                              5                            2.3828                                                                              5   2.7151                                                                              5            2.3796                                                                              5   2.6015                                                                              6   2.4977                                                                              3                            2.0536                                                                              3   2.5928                                                                              5            1.9984                                                                              11  2.4077                                                                              5   2.4717                                                                              5                            1.9980                                                                              11  2.4984                                                                              3            1.9782                                                                              10  2.3915                                                                              5   2.4010                                                                              5                            1.9766                                                                              11  2.4746                                                                              5            1.9401                                                                              3   2.3807                                                                              5   2.3777                                                                              5                            1.9396                                                                              3   2.4013                                                                              4            1.9029                                                                              3   2.0022                                                                              10  2.3043                                                                              2                            1.9059                                                                              3   2.3831                                                                              5            1.8613                                                                              4   1.9887                                                                              7   1.9984                                                                              11                           1.8597                                                                              4   2.3106                                                                              3            1.8175                                                                              2   1.9834                                                                              8   1.9806                                                                              12                           1.8421                                                                              3   1.9999                                                                              10           1.7582                                                                              2   1.8439                                                                              4   1.9432                                                                              3                            1.8354                                                                              2   1.9825                                                                              9            1.7528                                                                              2   1.8397                                                                              4   1.9074                                                                              3                            1.8179                                                                              2   1.9418                                                                              3            1.7446                                                                              3   1.8324                                                                              4   1.9016                                                                              3                            1.7589                                                                              3   1.9062                                                                              3            1.6610                                                                              3   1.6628                                                                              4   1.8595                                                                              3                            1.7464                                                                              3   1.8621                                                                              5            1.6507                                                                              3   1.6547                                                                              3   1.7613                                                                              2                            1.6578                                                                              4   1.8289                                                                              3            1.6165                                                                              2   1.4565                                                                              4   1.7575                                                                              3                            1.6504                                                                              4   1.7567                                                                              3            1.6010                                                                              3   1.4544                                                                              0   1.7538                                                                              0                            1.6029                                                                              3   1.6615                                                                              3            1.5519                                                                              2   1.3903                                                                              4   1.7444                                                                              2                            1.4896                                                                              2   1.6544                                                                              3            1.4531                                                                              4            1.6605                                                                              4                            1.4530                                                                              5   1.6501                                                                              3            1.4432                                                                              2            1.6522                                                                              3                            1.4359                                                                              3   1.4807                                                                              3            1.4361                                                                              3            1.6168                                                                              2                            1.4151                                                                              2   1.4539                                                                              4            1.4130                                                                              2            1.6040                                                                              2                            1.3854                                                                              0   1.4377                                                                              4            1.3852                                                                              0            1.5557                                                                              2                            1.3521                                                                              2   1.4149                                                                              4            1.3547                                                                              2            1.5108                                                                              2                                     1.4046                                                                              3            1.3524                                                                              2            1.4923                                                                              2                                     1.3864                                                                              4                              1.4541                                                                              4                                     1.3738                                                                              4                              1.4378                                                                              3                                     1.3556                                                                              3                              1.4031                                                                              2                                                                         1.3872                                                                              3                                                                         1.3557                                                                              2                                                                         1.3538                                                                              2                                                                         1.3517                                                                              2                            __________________________________________________________________________

                                      TABLE 5                                      __________________________________________________________________________          Aerosil                                                                            H.sub.3 BO.sub.3                                                                   SiO.sub.2 /B.sub.2 O.sub.3                                                           NaOH                                                                               % SiO.sub.2                                                                         % B.sub.2 O.sub.3                                                                   SiO.sub.2 /B.sub.2 O.sub.3                                                           % Na                                    Examples                                                                            g   g   employed                                                                             g   found                                                                               found                                                                               found found                                   __________________________________________________________________________     7    80  7.6 22    7.35                                                                               90.1 4.65  22.6 3.08                                    8    80  3.6 44    3.7 94.9 0.78 142.5 1.05                                    __________________________________________________________________________

EXAMPLE 9

A mixture of 60 parts of the ZBH borosilicate zeolite prepared in Example 2, using diethylene glycol dimethyl ether, and 40 parts of boehmite is extruded and subjected to exchange in 20% strength NH₄ Cl solution, in a ratio of 1:15, for 2 hours at 80° C.

80% strength methanol is 100% converted at 450° C. at a weight hourly space velocity of 7.8 h⁻¹. The yields, based on CH₂ employed, are:

    ______________________________________                                                        %                                                               ______________________________________                                         CH.sub.4          1.5                                                          C.sub.2 H.sub.4   4.1                                                          C.sub.2 H.sub.6   0.1                                                          C.sub.3 H.sub.6  25.0                                                          C.sub.3 H.sub.8   0.8                                                          C.sub.4 hydrocarbons                                                                            17.6                                                          C.sub.5 hydrocarbons                                                                            46.7                                                          ______________________________________                                     

We claim:
 1. A process for the preparation of crystalline ZBH borosilicate zeolites of the pentasil type which comprises: adding silicon dioxide, boric acid and an alkali metal salt to a liquid ether or ether-water solvent wherein the ether is selected from the group consisting of monoethylene, diethylene, triethylene and tetraethylene glycol dimethyl ether, diethyl ether, a mixture of triethylene to decaethylene glycol methyl isopropyl ethers, diethylene glycol methyl isopropyl ether, a mixture of polyethylene glycol methyl isopropyl ethers, a mixture of oxyethylated oxoalcohols having a mean molecular weight of 200, 600 or 6,000, and dimethoxymethane, the molar ratio of SiO₂ to B₂ O₃ being from 3 to 300, the molar ratio of alkali metal salt to B₂ O₃ being from 1 to 3 and the molar ratio of ether to B₂ O₃ being from 18 to 390, and thereafter heating the resultant solution to a temperature of from 80° to 140° C. in a closed vessel under autogenous pressure to form said ZBH borosilicate zeolites, wherein the zeolites have the formula

    M.sub.2/n O:B.sub.2 O.sub.3 :x SiO.sub.2 :y H.sub.2 O

where N is one or more cations of valency n, x is ≧10 and y is from 0 to
 80. 2. The process of claim 1, wherein the process takes place in a stirred autoclave under autogenous pressure.
 3. The process of claim 1, wherein the solution is heated at from 80° to 140° C. for a period of from 5 to 7 days.
 4. The process of claim 1, wherein the solution is heated to a temperature of from 110° to 130° C.
 5. The process of claim 1, wherein the molar ratio of SiO₂ to B₂ O₃ is from 10 to
 50. 6. The process of claim 1, wherein the molar ratio of alkali metal salt to B₂ O₃ is from 1.3 to
 2. 7. The process of claim 1, wherein the solvent used is diethylene glycol dimethyl ether or a mixture thereof with water.
 8. The process of claim 1, wherein the solvent used for the crystallization is triethylene glycol dimethyl ether or a mixture thereof with water. 